1. Field
The embodiments described below relate generally to systems for delivering radiation treatment. More specifically, some embodiments are directed to treatment verification systems used in conjunction with such delivery.
2. Description
Radiation treatment plans are designed to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. These goals might not be achieved if the radiation is not delivered exactly as specified by the treatment plan. More specifically, errors in radiation delivery can result in low irradiation of tumors and high irradiation of sensitive healthy tissue.
Delivery errors may arise from many sources. For example, a patient position may vary from that designated by a treatment plan, and/or internal patient anatomy may be displaced with respect to external visible markers. Current trends point to hypofractionated delivery in which high doses are delivered per each treatment fraction. These trends increase the necessity of positioning of the patient such that the target coincides with the isocenter of the radiation delivery device during any given treatment.
Commonly-assigned co-pending U.S. Patent Application No. 60/995,828 which is hereby incorporated by reference for all purposes, describes a system to verify a patient position prior to radiation delivery using tomographic images. The tomographic images are generated by a radiation detector which successively receives radiation from several radiation sources disposed in a fixed relationship relative to one another.
The field of view about the patient isocenter and the tomographic angular sampling range of such a system are determined by the relative locations of the radiation detector, the radiation sources and the isocenter. Generally, moving the radiation sources apart (i.e., away from the central radiation beam axis) will increase the angular sampling range (and the depth resolution of the resulting tomographic image) but decrease the field of view. Conversely, decreasing the source spacing will decrease the angular sampling range and increase the field of view.
A system's particular geometric arrangement of radiation sources, detector, and isocenter provide one characteristic field of view and one characteristic angular sampling range. These characteristics may reflect a compromise between conflicting imaging requirements of the various intended uses of the system. This compromise may be further constrained by detector size limitations and tight clearances between system elements.
In view of the foregoing, what is needed is a radiation treatment system to efficiently provide digital tomosynthesis having a first field of view and angular sampling range, and at least a second field of view and angular sampling range. The first field of view and angular sampling range may be suitable for one radiation treatment scenario and the second field of view and angular sampling range may be suitable for another radiation treatment scenario.